Since Ge has a higher carrier mobility than Si and a poor stability of a Ge oxide may be overcome by using a high k dielectric, Ge which is used as an advanced material of a device substrate or a channel has attracted much attention. However, by directly depositing the high k dielectric on a Ge surface cleaned with a dilute HF solution, a device generally has disadvantages of high interface charge trap density and large leakage current. An interface problem between the high k dielectric and a Ge substrate is a critical issue because of a poor thermal stability, a water solubility and a poor electrical performance of the Ge oxide. In order to solve this problem, many solutions have been presented, for example, including adding a GeO2 or GeOxNy interface layer, performing a sulfidizing treatment for the Ge surface, and doping fluorine ions in the interface. However, the high interface charge trap density and large leakage current are not effectively improved by the above solutions.